Ball joints are widely used for a connection part having a function of a spheroid joint.
FIG. 1 is a cross-sectional view illustrating a configuration of a conventional ball joint.
As shown in FIG. 1, the ball joint generally includes a ball stud (10) serving as a spheroid joint, a ball seat (20) which surrounds the ball stud (10) to protect the ball stud (10) and controls a friction force acting between the ball stud (10) and a socket (40), the socket (40) in which the ball stud (10) and the ball seat (20) are mounted, a plug (30) which seals the ball stud (10) to prevent a downward movement of the ball stud (10) under the socket (40) by a compressive load, and a dustcover (60) which covers an upper portion of the socket (40) to prevent dust from entering the ball stud (10), and caulking is performed on a lower end portion of the socket (40) and the ball joint is pressed on and inserted into a knuckle or arm to be assembled.
To prevent foreign materials from entering the vicinity of the ball stud (10) mounted in the socket (40), the ball joint is provided with a plug (30) on a lower end of the socket (40) as well as the dustcover (60) for sealing.
To manufacture such a conventional ball joint, the ball stud (10), the ball seat (20), and the plug (30) are inserted into the inside of the socket (40) and coupled with each other by assembling the separately processed ball stud (10) and the ball seat (20), inserting the assembled ball stud (10) and ball seat (20) into the socket (40), covering a lower opening of the socket (40) by the plug (30), and caulking a lower end portion of the socket (40).
However, according to the above manufacturing method, since the ball seat (20) is manufactured separately and then is assembled in the socket (40) using a complex assembly process such as caulking, etc., the productivity thereof can be lowered.
Meanwhile, in order to manufacture a ball seat using an injection molding method, only when the ball stud (10) with only a spherical surface without an aspherical surface is used, rotation of the ball stud (10) can be easily achieved after the ball joint is manufactured.
A conventional method of manufacturing the above-described ball stud provided with only the spherical surface without the aspherical surface will be described with reference to FIG. 2.
FIG. 2A is a view illustrating a ball stud processed by machining, and FIG. 2B is a view illustrating a ball stud manufactured by welding.
Referring to FIG. 2A, the ball stud (10) is provided with a stud portion (12) and a spherical head portion (13), and a portion of the spherical head portion (13) in contact with a ball seat is provided with a spherical surface. In this case, the spherical head portion (13) is formed to have the spherical surface by machining. As a result of the machining, a protruding portion is formed to have a vertex (13a) at the center of a lower end portion of the spherical head portion (13), thereby generating an interference with an inner side surface of the ball seat formed by injection molding, which influences on the quality of a product, and additionally requiring performing a separate treatment process to remove the vertex (13a).
Referring to FIG. 2B, welding and coupling are performed on a welding portion (12a) of the stud portion (12) and a welding portion (13b) of the spherical head portion (13) having a spherical surface. As described above, when the stud portion (12) and the spherical head portion (13) are coupled by welding and a shear load acts on the welding portions, cracks are generated in the welding portions by a shearing action, and thus a welding-type ball stud can be used for only some products subject only to a low shear load.
As described above, for manufacturing the ball stud without the aspherical surface, the above described problems occur, and even when the ball stud is manufactured without the aspherical surface, after the ball seat is formed by injection molding, the ball seat contacts the spherical surface of the spherical head portion throughout, thereby generating an excessive torque while rotating the ball joint.
Further, the dustcover (60) is coupled with an upper end portion of the socket (40). Since a dustcover coupling portion in a groove shape should be formed in the socket (40) for coupling the dustcover (60) using a separate process, many processes are needed for processing the socket (40).